Hi Arne.
I expressed the lowest note on the highland pipes as 8/7 rather than a 7/4 because it is below the tonic note.
This interval I agree is a lot flatter than an ET tone down. It is the interval that a barbershop singer would sing in a seventh chord.
Bellow is one of Harry Partch's "insipient tonality diamonds". All the intervals played together diagonally from the bottom corner up towards the right produce perfect Major seventh chords, and from the bottom towards the left produce perfect Minor seventh chords in downwards order. This uses all the simple ratios within the limit of 7, giving 4 Major Seventh and 4 Minor Seventh Chords (and of course 4 Major and 4 Minor chords   

                         7/7
                      12/7 7/6
                   10/7 3/3 7/5
                   8/7 5/3 6/5 7/4
                     4/3 5/5 3/2
                      8/5 5/4
                         1/1

I hope this makes things clearer (I've got to admit it totally confused me when I first came across it, but its worth persevering with).
The above is from Harry Partch's book "Genesis of a music", well worth a read if your interested in Just scales and Harmony.

All the best PP.